New Device Connected in the middle of the Night??

I have been an Xfinity customer for a long but lately, I am not experiencing the awesomeness I used to experience a couple of years ago. I pay for high speed (up to 400 Mbps), use only one-two device, recently paid additional to get XFI Pod, and yet the connectivity and speed are horrible. Yesterday my Internet stopped working and I rebooted the router and refreshed wifi connection etc but I gave up.  Then I see a notification from Xfinity saying "New Device Connected" ARRIS just connected to your home network for the first time. Name and Assign it for more control". This is what I noticed when I clicked on my Wi-Fi Network:

My Wi-Fi network appears to be secure but it says "Weak Security".  It then asks me to configure the router to use WPA2 (AES or WPA3 type). I have no idea what is this and why it happened and how can I fix it?

This is very annoying and I want to make sure I bring it to your attention before making the switch. What is going on?

 

Can anyone explain what is going on?